Thickening of glomerular basement membrane (GBM) and accumulation of GBM-like material in the mesangial matrix in the early stages of insulin-deficient diabetes probably results from increased synthesis of GBM-collagen and of glomerular glycoproteins. These changes are accompanies by an increase in glomerular and renal size and by supranormal renal functon. Shortly after the induction of experimental diabetes, uracil ribonucleotides synthesis de novo is increased in the whole renal cortex and in the glomerulus. This metabolic alteration, similar to that observed in renal compensatory growth, results in expansion of the cortical pool of uridine triphosphate (UTP), the sugar derivatives of which are required in the formation of both the collagenous and non collagenous moieties of GBM. The major objective of this research is to study the relationship between pyrimidine metabolism and the synthesis of GBM in glomeruli using rats with streptozotocin-induced diabetes. This approach will permit an examination of the role of increased bioavailability of UTP and uridine diphosphosugars in the abnormal synthesis of GBM in diabetes. Experiments in vitro will study the generation of nucleotides and the incorporation of radiolabeled precursors into UTP and uridine diphosphoglucose (UDPG) in isolated glomeruli. The effects of inhibitors (pyrazofurin, 6-aza uridine, N-(phosphonacetyl)-L-Aspartate) or stimulators (orotate) of UTP and UDPG formation will be investigated in isolated glomeruli directly in vitro and in glomeruli obtained after long-term infusions in chronically cannulated animals. GBM synthesis will be estimated by the rate of incorporation of infused radiolabeled lusine into GBM-lysine and control conditions and following manipulation of pyrimidine metabolism. Factors influencing the interpretation of results such as glomerular blood flow, plasma specific redioactivity of the infused precursor and the size of the aminoacid precursor pool will be evaluated in independent experiments.